Cassini Mission Science Archive

April 12, 2005
Date taken: December 12, 2004
Distance from Saturn: 1.8 million kilometers (1.1 million miles)

This photograph of Saturn’s rings includes a great deal of information that might not be apparent at first glance. It offers another clear example of the benefits of getting extremely close-up when trying to understand the objects in our solar system. You are actually looking up at the ring plane—as the rings in this image are tilted away from Cassini at an angle of about 4 degrees. Click for a high-resolution version of the image.

Look closely at the image and you’ll discover at least six prominent gaps in the ring system along with at least 10 significant variations in ring color. The rings are also clearly three-dimensional with particles rising and falling from the plane of the rings due to gravitational forces that cause ring particles to bunch up in some places. If you look very closely at the lighter colored section you’ll see distinct wave-like features in the rings. All of these anomalies in what used to look like a smooth and flat ring plane suggest that the ring particles are constantly interacting with each other and responding to the presence of the various moons in Saturn’s system. In other words, the Saturnian system is a very lively place, indeed, with constant interaction among its different components.

For a close-up animation showing a fly-over of this image go to the NASA website and study the rings up close as they move by. The file is about 5.5 megabytes but well worth the wait. The animation lasts for about 25 seconds.

March 14, 2005
Date taken: September 2004
Distance from Saturn for the animation: 71 million kilometers (44 million miles) to 46 million kilometers (29 million miles)

Scientists on the Cassini-Huygens team are learning a lot about the complex processes that control the behavior of Saturn’s atmosphere. Today’s photo shows a large bright object that scientists call the "Dragon Storm.” Look just to the right of the center of the image. By studying Saturn’s atmosphere over many months scientists discovered that the Dragon Storm periodically flares up and then subsides over time. It apparently behaves like an electrical storm with lightning and rain and seems to maintain its energy between the flare-ups that the Cassini spacecraft captures.

Using images captured between February and March 30, 2004 the Cassini team created a movie of storm formation in Saturn’s atmosphere.

Click for the animation.

A lot is going on in the movie and you’ll have to watch carefully to fully appreciate everything that’s happening. Just to the right of the image center you’ll see the flare-up of a major storm similar to the Dragon Storm. You’ll also note the merging of two smaller storms, seen as small black dots that come together during the animation.

An experiment for home
Although Saturn’s atmosphere is very complex, scientists know that convection forces play an important role in creating the fascinating patterns that Cassini is discovering. Fortunately, convection is one process with which you can experiment right at home. Convection results when fluids of different densities move past each other in the process of transferring heat.

You can create a very simple version of Saturn’s atmosphere by taking a clear glass bowl of very hot tap water (please get adult help when you try this experiment) and placing that bowl inside a larger bowl filled with ice. Let the water settle for a moment so that it doesn’t slosh around in the bowl. Now, take an eyedropper and place one or two small drops of food coloring in the center of the bowl of hot water and one or two small drops near the edges of the bowl. Watch the food coloring for three minutes. Look at it from the top of the bowl and from the sides. Does the food coloring remind you in any way of Saturn’s atmosphere? Does it stay still or move? If it moves does it move faster in the center of the bowl or near the edges?

Send in a report that includes a clear description and photograph of your experiment along with a write-up of your observations AND your explanation for what you observed and the Science Center team will select one report to publish right here on the Cassini-Huygens web page.

February 28, 2005
The diversity of Saturn’s moons
Today’s release shows the benefits of getting a close look during the exploration of our solar system. The photographs, all taken with the Cassini spacecraft, show six Saturnian moons, varying widely in size and each with a distinguishing feature. Together they provide compelling evidence of the diversity within the Saturnian system.

Dione		Enceladus		Phoebe

• Dione (diameter 1,118 km, 695 mi) has shadowed craters and a contrasting area of bright, wispy streaks along with variations in brightness across its surface.
• Enceladus (diameter 505 km, 314 mi) has ropy, taffy-like topography created by a variety of horizontal forces near the surface of the moon.
• Phoebe (diameter 220 km, 140 mi) has many craters and lots of variation in brightness possibly caused when darker surface material collapsed to reveal underlying ice.

Iapetus		Mimas		Titan

• Iapetus (diameter 1440 km, 895 mi) has a spectacular landslide from material that appears to have collapsed from an area 15 kilometers high (9 miles) that forms the rim of an ancient 600-kilometer (375 mile) impact basin.
• Mimas (diameter 398 km, 247 mi) has its giant Herschel crater 130 kilometers wide (80 miles) with its prominent central peak, seen here almost exactly on the terminator. The impact that formed it probably nearly destroyed the moon.
• Titan (diameter 5,150 kilometers, 3,200 mi) has tributaries of flowing liquid (probably methane) from different sources emptying into a major river channel.

February 11, 2005
Surface temperatures on (1) Iapetus and (2) Phoebe
Date Taken: (1) Iapetus (left) Dec 31, 2004 (2) Phoebe (right) June 11, 2004

These temperature charts for Saturn’s moons Iapetus and Phoebe may look confusing. Scientists plotted the data for each moon onto a coordinate system that displays latitude and longitude and the black areas show regions where no data was collected. So, instead of having the familiar projections used for spherical objects the data appear to have jagged edges. Except for the missing data, they’re actually quite simple, just like the weather contour maps that you might see on television.

This week’s release shows how the physical characteristics for the different moons affect their surface temperatures. It’s a great example of how scientists use one set of data to help validate new results. Look at the asterisk on the Iapetus temperature map (on the left). It shows high temperatures of nearly 130 degrees Kelvin (that’s –226 Fahrenheit) at noon right on the equator. By contrast the much colder temperatures on the moon Phoebe peaked near 112 Kelvin (-258 Fahrenheit). Both moons are approximately the same darkness with material that absorbs nearly the same amount of sunlight, and both moons (being in orbit around far-away Saturn) are essentially the same distance from the sun. So, why do scientists observe such a big temperature difference between the two moons? It’s because of the rotation period. Phoebe’s rotation period of 9 hours is much faster than Iapetus’ rotation period of 79 days. Therefore, the surface of Phoebe has much less time to heat up during the day.

January 21, 2005
Date Taken: (1) Probe zoom shot (Dec 25, 2004); (2) Images of Titan (Jan 14, 2005)
Distance from Saturn’s moon Titan: 16 kilometers and 8 kilometers
This week’s release showcases the Huygens probe that was released by the Cassini spacecraft in order to provide detailed studies of Saturn’s largest moon, Titan. Shrouded in an atmosphere that’s 10 times thicker than Earth’s, Titan is the only major object in our solar system whose surface remained largely a mystery—at least until the Cassini mission started chipping away at what lay beneath Titan’s thick haze.

Huygens probe zoom-shot		Huygens images of Titan

The image on the left shows the Huygens probe about 12 hours after Cassini pushed it on its way to Titan. The image is a close-up showing the probe headed directly to its destination as it pulls away. The probe’s heat faces away from us and we’re looking at the structure that houses the instruments on the probe from this vantage point. The main Cassini spacecraft followed the probe for two days and then changed its course in order not to follow the probe into Titan’s atmosphere.

The three-image set on the right shows the pictures returned by the Huygens probe as it descended through Titan’s atmosphere. The upper left image was taken when the probe was at an altitude of 16 kilometers and appears to clearly show drainage channels that lead to some type of shoreline. You can just imagine streams of liquid methane leading to an icy cold methane lake. But, scientists will need more time to determine exactly what’s shown in the photo.

The photo on the bottom left was taken when the probe got down to an 8-kilometer distance from Titan’s surface and may actually be the landing site. The picture seems to show high ground and flooded low-lying areas. Scientists have determined that Huygens landed with a big “splat” indicating that it may be stuck in “mud” – almost surely not the kind of mud that anyone on Earth has ever imagined.

Finally the image on the far right shows the actual surface of Titan. The big rock-looking objects are actually ice blocks but their size and distance from the probe have yet to be determined. Additional information about the Huygens probe can be obtained from the official NASA Cassini website.

December 31, 2004
Date Taken: October 27 and December 14, 2004
Distance from Saturn’s moon Dione: see below
This week’s release shows two photographs of Saturn’s moon Dione, which was first discovered by Cassini in 1684. With a diameter of 1,118 kilometers (695 miles) Dione was the fifth Saturnian moon discovered and is one of four Saturnian moons clustering in size between 1,000 - 2,000 kilometers in diameter.

The image on the left was taken on October 27 when the Cassini spacecraft was at a distance of 1.2 million kilometers (746,000 miles) from Dione. The second image was taken on December 14th during the spacecraft’s closest approach (so far) to the moon (81,400 kilometers or 50,600 miles) and shows amazing details of the region that scientists call “wispy” because of the white streaks.

Look closely and notice that the right side of the moon presents a different appearance from the left. The left side shows clearly defined craters. Look even more closely and you’ll see craters within larger craters. Now compare these markings with the long linear streaks on the right side of the image. You can still see craters on the right side of the moon but they are traversed by these linear streaks that run for distances of tens of kilometers. The Cassini imaging scientists expected these brighter streaked areas to be composed of thick ice deposits, but now conclude that they result from fractures in the surface of Dione caused by tectonic forces. Additional information about Saturn’s moon Dione can be obtained from the official NASA website.

December 24, 2004
Date of Event: December 24, 2004
December 24 marks the release of the Huygens probe that will plummet through the atmosphere to the surface of the giant moon Titan. This long-awaited event is a nail-biter both for the team at JPL and the scientists at the European Space Agency. ESA designed the Huygens probe and NASA’s Cassini spacecraft served as the “bus” that carried the probe to the Saturnian system during its seven-year voyage.

The image on the left below shows an artist’s rendering of the probe shortly after separating from the Cassini spacecraft. It shows the trailing side of the probe as it pulls away. The image on the right shows the probe’s forward side with its “nose-cone” shape designed to dissipate heat during entry into Titan’s thick atmosphere.

Don’t forget to visit the Air and Space Gallery for a close-up look at the Huygens probe attached to the side of the full-scale Cassini spacecraft—on loan to the Science Center through the courtesy of NASA-JPL.

When NASA engineers signal the spacecraft, a set of tension-loaded springs will gently push the Huygens probe away from Cassini. The team should get confirmation of the successful release at about 8:00pm PST on December 24th. Click here and then look under the heading “Featured Videos” and select the last choice under that heading called “Huygens Probe to Titan (Quick Time Stream)” to see a cool animation of the probe separation and to hear from the key scientists in charge of this part of the mission.

Once the separation occurs, both craft will remain on a direct course for Titan to assure that the Huygens probe takes a successful path straight for its target. As a result of its gentle push, the two craft will slowly separate until NASA calculates that it is safe to command the Cassini spacecraft to peel away from the pathway that would cause it to follow the Huygens probe into Titan – a sure disaster. The project team will order that change in Cassini’s path on December 27th. Cassini will then swing around Titan, using the moon’s gravity to guide its path, and head for another trip around Saturn.

December 1, 2004
Date Taken: November 9, 2004
Distance from Saturn: 6.3 million kilometers (4 million miles)
This week’s release is another great example of how scientists can create a more complete understanding of Saturn’s rings by using relatively simple data. It might be surprising to learn that the picture below is not an actual photograph of the rings. For an explanation, imagine for a moment that you’re riding in a car while staring at a picket fence. A light is behind the fence. As you go along you’ll see the light appear to blink on and off as you alternate between looking directly at the fence and the spaces between the slats. If the slats in the fence are not evenly spaced, or if they vary in thickness, you’ll also notice that the on-and-off flickering of the light presents an uneven appearance. For example, you will observe light for a slightly longer period when the fence slats are farther apart. If the slats are thin and evenly spaced you will observe a more frequent flickering of the light than if the slats are thicker and evenly spaced.

This week's release is actually a false color image that was created when the Cassini spacecraft measured the brightness of the star Xi Ceti as Saturn’s rings passed in front of the star. The rings represent the slats in the picket fence. Scientists converted this data into a false color image that shows important information about the rings—namely that the material in the rings is not evenly spaced.

The moons that orbit Saturn have a profound effect on the manner in which the material in the rings gets distributed. According to the color assignment chosen by the NASA scientists, bright areas represent the denser regions of the rings. The denser area on the left of the image results from the gravitational influence of Saturn’s moon Janus. The denser area toward the right side of the image results from the moon Pandora. For other images of the rings of Saturn, see the official NASA website.

November 12, 2004
Date Taken: July 2, 2004 (data release date)
Distance from Saturn: estimated 1,206,000 kilometers (754,000 miles)
Sometimes data in graph form appears less interesting than an actual photograph of Saturn itself, or its rings or moons—all of which are things that we can actually see. Plus graphs can be challenging to read because it may not be obvious how to interpret the axes. However, graphs let scientists build pictures of things that can be measured but not seen – like temperature and wind speed. So, by color coding the information and laying out the data in the right fashion we can actually “see” temperature and wind speed on Saturn.

The top graph shows Saturn’s atmospheric temperature. It was measured by the Cassini spacecraft’s composite infrared spectrometer. The horizontal axis shows the equator down to the south pole of the planet. The vertical axis shows altitude above the cloud tops—increasing in the upward direction. The color code shows that temperatures increase from blue to greenish-yellow through red.

The graph shows a temperature division between the layer just above the cloud deck (troposphere) and the layer above the troposphere (called the stratosphere). The troposphere is cooler and relatively constant in temperature all the way from the equator down to the south pole. The stratosphere is warmer than the troposphere and shows a relatively constant temperature from the equator down to about 45 degrees south latitude at which point it gets even warmer as shown by the red color. This rise in temperature near the south pole makes perfect sense because at this point in its orbit Saturn is tilted so that the southern hemisphere of the planet shows more prominently. Recall that the Cassini-Huygens spacecraft approached the planet from the south and had to cross the ring plane.

The bottom graph was largely derived from the data collected in the upper graph and shows Saturn’s wind speed in the same physical region above the could tops – namely from the troposphere up through the stratosphere and in the latitudes ranging from the equator down to the south pole. The graph shows that the winds move faster near the equator (they actually circle the planet from east to west but that wouldn’t be obvious from this graph alone). They drop quickly by about 140 meters per second (300 miles per hour) when you cross into the region below about 25 degrees south latitude and then they remain relatively constant down to the south pole. Scientists do not yet know the reason for the reduction in wind speed. For technical details on these images see the official NASA website.

October 29, 2004
Date Taken: October 26, 2004
Distance from Saturn's moon, Titan: 450,000 kilometers (280,000 miles)
The image below was captured as the Cassini-Huygens spacecraft raced towards its close encounter with Saturn’s largest moon, Titan. The photograph is a study of the moon’s atmosphere and not its surface features. The image was actually built up from four images acquired through different color filters and this allowed NASA scientists to create a final image by assigning false colors to bring out contrasts.

The red and green areas illustrate a contrast because the methane in Titan’s atmosphere absorbs light by different amounts depending upon where you look. The pretty blue ring around the edge shows the high atmosphere and detached hazes. If you look carefully at the photograph you can get a good feeling for just how far Titan’s atmosphere reaches out into space.

October 15, 2004
Date Taken: July 2, 2004
Distance from Titan: approximately 1,206,000 kilometers (754,000 miles)
Today’s Cassini-Huygens image tells us about the invisible magnetic field surrounding Saturn. Since a magnetic field can suggest a lot about what goes on deep in the hot molten core of a planet, scientists are very interested in such measurements. The graph looks pretty confusing at first glance, but the data is actually very easy to interpret if we first take a moment to understand exactly what the Cassini spacecraft is measuring.

If you’ve ever played with a magnet you most likely know that its magnetic field extends for a small distance into the surrounding space. If you want to test this statement, just place a strong magnet on a flat surface about a foot away from a small paper clip. Slowly move the magnet toward the paper clip and see what happens.

You may also know that charged particles (electrons and ions) are influenced by a magnetic field – i.e. their motions are affected by the presence of the field. There is a wonderful hands-on exhibit in the Creative World gallery here at the California Science Center that will let you test the effects of a magnetic field on charged particles.

This basic concept (magnetic fields influencing the motion of charged particles) plays out on an enormous scale in the Saturnian system because Saturn itself has a strong magnetic field which extends far into space, and the Sun is a reliable source of charged particles that stream into space at speeds ranging from 300 – 1000 kilometers per second. When this stream of charged particles, which scientists call the solar wind, slams into the magnetic field surrounding Saturn, a shock wave is formed on the side facing the sun and a long tail streams out from the side of the planet that faces away from the sun. Since the planet’s magnetic field deflects the solar wind a huge bubble results, which scientists call a magnetosphere (or magnetic bubble).

Saturn, its rings and moons are nestled inside the bubble within a giant hollowed out area protected from the solar wind by the strength of the planet’s magnetic field. Since the magnetosphere and magnetic field are linked, the scientists on the Cassini mission have yet another window into the core of the giant ringed planet.

The magnetosphere has several components. The place at which the solar wind first meets Saturn’s magnetic field is called the bow shock. The region adjacent to the bow shock is the magnetosheath. The area immediately behind the magnetosheath is the magnetopause.

In today’s graph (the first figure above), Cassini has crossed the bow shock and is moving through the magnetosheath and on through the magnetosphere. The upper graph shows the strength of the magnetic field. The lower graph shows the intensity of charged particles (green is higher intensity). So you can see that the particle intensity is greatest in the area of low magnetic field strength and that the particle intensity drops off significantly in areas where the magnetic field strength is greatest. For lots of technical details on these discoveries, see the official NASA website.

September 29, 2004
Date Taken: July 2, 2004
Distance from Titan: 1,222,000 kilometers (759,316 miles)
Cassini-Huygens took these images two days after crossing the ring plane of Saturn as the spacecraft entered into the first of 40 planned orbits around the planet. The series offers an unusually good example of the value of looking at objects in different wavelengths and each wavelength is represented by its own false color. Notice the terminator where the day and night meet. The sunlit side of the moon is the left side of each image and the night is shown on the right.

Start with the crescent-shaped image on the left, and note how the diameter of the image is smaller than for the other three images in the set. This is because the wavelength selected for this image cuts through to the surface of the moon ignoring Titan’s huge atmosphere. The result shows the surface of the moon only. In contrast the green image uses a wavelength (3.3 microns) that is sensitive to the methane in Titan’s atmosphere. The atmosphere extends for more than 700 kilometers (435 miles) above the surface and the wavelength is beyond the realm of human vision. The red image shows the presence carbon monoxide in Titan’s stratosphere, which is relatively warm and extends to a distance of 200 kilometers (124 miles) above the surface. This image was also created using a wavelength beyond the range of human vision—namely 4.7 microns. Finally, The multicolor image on the far right shows Titan’s surface along with the carbon monoxide and methane regions of the atmosphere in a single image. The circle shows Titan's actual surface. For lots of technical details on these discoveries see the official NASA website.

August 20, 2004
Date Taken: June 1, 2004
Distance from Saturn: 16.5 million kilometers (10.3 million miles)

Until planetary scientist Dr. Sebastien Charnoz and imaging team member Dr. Andre Brahic (University of Paris) released their latest findings there were only 31 known moons orbiting Saturn. The Charnoz-Brahic discovery increases that number by two. Only 48 days into a four-year mission, the odds are high that the scientists on the Cassini-Huygens team will discover even more moons in the months ahead. This is one of the more interesting NASA images even thought it may look confusing at first glance. Using animation it’s possible to understand how astronomers discover new objects. Dr. Carolyn Porco, the imaging team leader at the Space Science Institute in Boulder, Colorado, planned out the imaging sequences that led to the Charnoz-Brahic discovery. The discovery of new moons in the Saturnian system is one of her major objectives. To meet Dr. Porco and learn more about the two moons, click here.

Examine the two images above and notice the small square as it moves in a clockwise direction. Separate animations apply for each moon. The square traces the path of the newly discovered satellite across a background of stars and other objects. The image sequence was taken before Cassini crossed Saturn’s ring plane, so the view is from the southern hemisphere looking upward at the brightly lit (and deliberately overexposed) side of the rings. Without the ability to distinguish the motion of one individual speck against the cluster of other objects, scientists would be hard-pressed to determine the orbit of something so tiny. Dr. Charnoz created a computer code to handle that complex problem and actually made the discovery using his laptop while on vacation. For lots of technical details on these discoveries see the official NASA website.

July 30, 2004

Date Taken: July 3, 2004
Distance from Titan: 789,000 kilometers (491,000 miles)
This week’s image is a great example (on a really large scale) of fluid separation because of differences in density. It brings to mind those wonderful classroom experiments in which alcohol, oil and water, each colored differently, separate into distinct layers because of their differences in weight.

The image shows Titan’s atmosphere divided into two thin haze layers. (If your monitor is dark, you may need to increase the brightness to see the outer layer.) The outer haze layer is actually detached and appears to float high in the atmosphere. The image uses false colors to enhance visibility. Titan's haze forms from a process that begins at altitudes above 400 kilometers (250 miles). This is where ultraviolet light breaks down methane and nitrogen molecules. Scientists think these products react to form complex organic molecules containing carbon, hydrogen and nitrogen. These then form the very small particles seen as haze. The bottom of the detached haze layer is a few hundred kilometers above the surface and is about 120 kilometers (75 miles) thick.

It’s amazing that the moon of a planet a billion miles away has a tiny part of its atmospheric chemistry that’s not entirely different from what goes on in the Earth’s atmosphere. The figure below shows a comparison of the atmospheres of Earth and Titan. Look carefully at the vertical scale on each graph below, and notice that Titan’s atmosphere extends about 10 times farther into space than Earth’s atmosphere.

For details on the chemical process that causes Titan’s hazy upper atmosphere see NASA's official Cassini site.

July 9, 2004

Date Taken: June 30th during orbit insertion
Distance from Saturn: 16,000 kilometers (estimate) (10,000 miles)
This week’s image shows an extreme close-up of Saturn’s rings that tells us something pretty cool about their composition and allows for some fun detective work. The image has a spatial resolution of about 97 kilometers (60 miles). This is not sufficient to reveal the individual particles within the rings (since scientists estimate the largest of these to be house-sized), but interesting patterns clearly emerge. Consider the slight curvature in the rings. Concentric and bending ever so slightly, they suggest a radius pointing to the left as the location of Saturn itself.

The vibrant colors also give us a hint and suggest a differentiation of some type. The data is from the Ultraviolet Imaging Spectrograph, built and operated by a team from the University of Colorado at Boulder. The coloration shows the variation of concentrations of dirt in the rings, which are largely composed of water ice, and which get cleaner as the distance from Saturn increases. The separation between the C and B rings occurs at about the middle of the photograph and the B-ring is to the right of the image. For more information on the rings of Saturn see NASA's official Cassini site.

June 29, 2004

Date Taken: Artist's rendering
Distance from Saturn: 160,000 kilometers (99,278 miles)
This artist's rendering depicts the upcoming event that scientists have eagerly anticipated for 7 years. It shows the Cassini-Huygens spacecraft immediately after crossing the ring plane of Saturn and just prior to orbit insertion. The ring crossing is scheduled to occur at approximately 7:11pm on Wednesday, June 30th. Recall from previous releases (see archive for May 14th and June 1st) that the relative position of Saturn shows a slightly tilted ring plane as the spacecraft approaches from the southern hemisphere. Cassini will cross the ring plane between the large gap that separates the F and G rings to end up in the northern hemisphere before firing its engine. About 25 minutes later the main engine on the spacecraft will start a 96-minute burn to reduce Cassini’s speed by 626 meters per second (1,400 miles per hour) so that Saturn’s gravitational field can capture it as an orbiting satellite. Without this reduction in speed, Cassini would speed past Saturn, its path being deflected by the ringed giant’s huge gravity, but without capture. It would then become another satellite of the sun as it moved away from Saturn and farther out into the solar system.

However, if all goes well, just 27 minutes after the main engine starts to fire Cassini will make the closest approach to Saturn of its entire 4-year tour, coming within 20,000 kilometers (12,427 miles) of the giant planet’s cloud tops. Shortly after the ring-plane crossing, the spacecraft will also take the highest resolution images of Saturn’s rings looking down on the rings from a distance of 16,000 kilometers (9,937 miles). For more artist renderings of Cassini at Saturn and its moons see NASA's official Cassini site.

June 16, 2004

Date Taken: June 11th (Cassini close approach to Phoebe)
Distance from Saturn’s moon Phoebe (closeup): 13,377 km (8,314 miles)
Distance from Saturn's moon Phoebe (full view): 32,500 km (20,200 miles)
These images of Saturn’s moon, Phoebe, are surprisingly captivating—perhaps even a bit startling. Think for a moment about what they mean and their impact perhaps becomes more evident. Phoebe is a tiny, tiny place in the scheme of things. Not even noticed until 1898. Fuzzy in all of the imagery acquired for the past 106 years, even with the much-improved resolution of the Voyager flyby in 1980, and still looking like a slowly growing fuzzy blob in the three-photo series of June 4th – 7th, which was released in last week’s update. Suddenly, thanks to the June 11th close approach of Cassini, we see stunning details on an object that measures only 220 kilometers in diameter and that took us seven years to reach. The photographs look almost like the results of a motion-picture special effects project, providing clear details on such a tiny object so far away.

The data itself points toward an icy moon covered by a dark, thin layer of material that has been blasted countless times by impacting bodies of various mass and diameter. The many impacts show the results of craters that blast fresh icy material out of the impact point, ejecting it out over the dark surface of the moon. The relative brightness of areas surrounding the many impact craters might lead to evidence of the timing of the impacts, with brighter areas representing more recent collisions.

Of particular interest is the completely battered nature of this irregularly shaped body. An object this tiny just doesn’t present a collision opportunity with great frequency unless it happens to be in an area of unusually high bombardment. Perhaps Phobe is very, very old, taking its truly rare impacts slowly over countless ages. Maybe scientists will determine that it’s much older than Saturn’s other moons. It will be interesting to see if they can determine the age of this unusual satellite with high accuracy. Recall that it orbits in a direction opposite to that of the other moons of Saturn, and that its orbital plane is inclined relative to that of the rings and other moons. For more information on this and other images of Phoebe see NASA's official Cassini site.

June 10, 2004

Date Taken: June 4th - June 7th
Distance from Saturn's moon Phoebe: 4.1 million kilometers (2.6 million miles) to 2.5 million kilometers (1.5 million miles)
This series of images show Saturn’s dark moon Phoebe as the Cassini-Huygens spacecraft approaches along a path that is almost a straight line between the sun and the tiny moon itself. The progression of images clearly shows the moon increasing in field of view as the spacecraft approaches.

Phoebe is a mysterious place that scientists have barely begun to explore. The tiny moon measures only 220 kilometers (137 miles) across and has a very dark surface that reflects only about 6 percent of the light that falls upon it. In addition to its mysterious appearance Phoebe orbits Saturn in a direction that is opposite to that of the other moons that revolve around the ringed giant. It also has an orbit plane that’s inclined to the plane of Saturn’s rings, making scientists suspect that Phoebe is a captured object - perhaps from the Kuiper belt. On Friday, June 11th Cassini will pass within 2,000 kilometers (1,240 miles) of the surface of Phoebe using its powerful cameras to photograph details as small as a few tens of meters across. This could be a real eye-opener as there is a great deal to learn about this tiny and mysterious place. For more information on this image see NASA's official Cassini site.

June 1, 2004

Date Taken:
Upper image (Hubble Space Telescope), March 22, 2004
Lower image (Cassini-Huygens spacecraft), May 16, 2004
Distance from Saturn's moon Titan: 24.3 million kilometers (15.1 million miles)
These images show the benefits of getting as close as possible in order to study the planets in our solar system. The differences between the two images are due mostly to the filters used and the viewing angle. The upper image was taken from Earth orbit using the Hubble Space Telescope and uses four filters to form an image that would be very close to what the eye would see through a telescope based on Earth. In this image the rings of Saturn are almost at their maximum tilt toward the Earth. The bands in Saturn’s atmosphere show up as pastel colors. The clouds are largely composed of ammonia and methane and exist at various altitudes.

The lower image, taken by the Cassini-Huygens spacecraft, uses three filters and shows the planet as the spacecraft approaches from 13 degrees below the equator. The details showing the structure of the planet’s atmosphere, along with the striking shadow and lighting effects that result from the camera’s viewing angle, offer a sharp contrast to the Hubble imagery. Saturn’s moon Enceladus, discovered by Herschel in 1789 with a diameter of 502 kilometers is visible just below the south pole. For more information on this image see NASA's official Cassini site.

May 25, 2004

Date Taken: May 5, 2004
Distance from Saturn's moon Titan: 29.3 million kilometers (18.2 million miles)
The most recent NASA release shows the mysterious moon Titan. With a diameter of 5,150 kilometers it is the largest moon of Saturn, first discovered by Christiaan Huygens in 1655. There is enormous excitement about this moon because it is the object of study for the detachable Huygens probe that will descend through the hazy atmosphere to whatever lies below – perhaps even a methane ocean. The coordinate system around Titan shows its orientation to the approaching Cassini-Huygens spacecraft. About 25 percent of the surface is illuminated in the photograph. We can probably expect a lot more imagery of Titan as the spacecraft continues on its journey, since the instruments onboard can show more detail than the best Earth-based images. For more information on this image see NASA's official Cassini site.

May 14, 2004

Date Taken: April 16, 2004
Distance from Saturn: 38.5 million kilometers (23.9 million miles)
The Cassini-Huygens spacecraft is really getting down to business with the release of this photograph. Too close for the narrow-angle camera to capture Saturn in full view, this image shows interesting details in the atmosphere of the ringed giant. Scientists believe that the dark spot at the south pole could be affected by Saturn's magnetic field because the field is nearly aligned with the planet's rotation axis. The different levels of shading and patterns suggest lots of activity in the atmosphere of the planet, in part because the cloud bands move at different speeds. Other interesting features include the two white spots visible above and to the right of the dark spot, and an oval-like feature that appears just above the top of the dark cloud band and which straddles the lighter area to the right. By the way, the dot to the left of the south pole is the moon Mimas. It was discovered by Herschel in 1789 and is the first of five Saturnian moons to be discovered having diameters between 180 and 400 kilometers. For more information on this image see NASA's official Cassini site.

May 7, 2004

Date Taken: (April 15th approx.)
Distance from Saturn: 39.1 million km (24.4 million miles)
This week’s release focuses on Saturn’s largest moon, Titan. The image is a little tricky to interpret because it combines images from the Cassini-Huygens spacecraft (taken in mid April) with an image compiled from data released by the Hubble Space Telescope in 1997-1998. The upper images were taken four days apart after Titan had rotated through an angle of 90 degrees. This means that the two halves, when combined, show one hemisphere of the moon. A coordinate system for Titan is shown superimposed on the images in the upper part of the photograph. It matches the coordinate system on the map shown at the bottom of the photograph. The map quantifies different surface reflectivity and matches the shading that you see in the images of the moon. Deep blue represents the darkest areas and deep red represents the lightest. For more information on this image see NASA's official Cassini site.

May 3, 2004

Date Taken: March 27, 2004
Distance from Saturn: 47.7 million kilometers (29.7 million miles)
This week’s NASA release shows Saturn in full view and natural color. Notice the orientation of the planet as seen by the approaching spacecraft. The sun is located to the right with the shadow of the planet cast against the rings to the left. Now look carefully at the angle of the terminator (where the sunlight meets the darkness) and you’ll see that the sunlight actually streams in from the lower right corner of the photograph. This angle is just right for the sunlight to slip between the gaps in the rings on the right side of the planet (that’s the famous Cassini gap) and shine on the upper atmosphere where you see the bright silvery streak.

Four of Saturn’s moons are also visible in the photo. Going clockwise from the top right they are Enceladus, Mimas, Tethys and Epimetheus. Sometimes the moons are very difficult to se. Here’s a hint that might help especially if you have a little dust on your screen. Move the image slowly up and down using the scroll bar or by grabbing the image frame. The “dust” particles that travel with the planet are the moons shown in the photo. It’s almost like observing the “wanderers” against the background of fixed stars (i.e. the dust on your screen). You can also click the image above to see one in higher resolution. For more information on this photograph check out NASA's official Cassini site.

April 26, 2004
Date Taken: April 3, 2004
Distance from Saturn: 44.5 million kilometers (27.7 million miles)
This week’s NASA release clearly shows the benefit of using different wavelengths of light for imaging the giant ringed planet. Saturn’s atmospheric gases absorb and scatter various wavelengths of light differently—as do the clouds (depending on their height and thickness). This allows the NASA imaging teams to create photographs that make selected features more prominent. Using the proper filters scientists can “peel away” the uppermost layers of Saturn and peer down into its fascinating atmosphere. Moving clockwise from the upper left the four images show Saturn in ultraviolet, visible blue, far infrared and near infrared (just beyond visible light). For more information on this series of photographs check out NASA's official Cassini website.

April 21, 2004

Date Taken: March 10, 2004
Distance from Saturn: 55.5 million kilometers (34.5 million miles)
Like trusted sheep dogs that keep members of their flock from wandering too far, this week’s NASA release shows the two moons whose gravitational influence keeps the F-ring confined to a narrow width of several kilometers. The moon Prometheus, only 102 kilometers (63 miles) across, is in the left center of the image just inside the ring. It keeps the F-ring from spreading inward toward Saturn. Pandora, which is a mere 84 kilometers (52 miles) across, is outside the ring above the center of the image. It keeps the F-ring from spreading outward, away from Saturn. Scientists still cannot fully explain the interactions between these moons and the F-ring, in part because the orbits of the moons can change unpredictably when they get very close to each other. The Cassini-Huygens spacecraft will study the orbits of Prometheus and Pandora over a period of time to help determine their masses and thereby enable more accurate models of their interactions with Saturn’s F-ring. For more information about this exciting image see http://saturn.jpl.nasa.gov.

April 9, 2004

Date taken: February 22nd through March 22nd, 2004
Today's NASA image was recorded over a period of 26 days and shows a rare event that has only been observed once before on Saturn. The images show the progress of two storms, each with diameters of about 1,000 kilometers (621 miles) that merged together. The four images on top record the storms as they approach each other. The four images on the bottom show the aftermath of their encounter. Notice how the resulting storm is initially stretched into an elliptical shape before settling down to a more circular form. If you look closely you can also see a halo of bright clouds surrounding the resulting storm. To learn more about this image click here.

April 2, 2004

Date taken: March 8, 2004
Distance from Saturn: 56.4 million kilometers (35 million miles)
Today's NASA image of Saturn reveals subtle details in the atmosphere of the planet at a location of 38 degrees south latitude. You'll need eagle eyes to see the two faint dark spots, but look closely. The first lies right on an imaginary line that connects the north and south poles of the planet. The second lies to right of the first spot about half the distance to the edge of the planet. This natural color image is a composite of separate exposures taken with the spacecraft's narrow angle camera. The imaging team at NASA enhanced the colors and contrast to help bring out the subtleties. Click for more information on this release.

March 26, 2004

Date taken: February 15 - Feb 19, 2004
Today's NASA release is an animation showing the motion of the clouds and haze high in Saturn's atmosphere. Click for the animation and more details. The 30 stacked images were collected over five days (Feb 15 - 19) using the narrow angle camera aboard the Cassini-Huygens spacecraft. The animation shows six complete 10.6 hour rotations of the ringed planet. The motions of the atmosphere show up best near the equator and southern latitudes. Watch the animations carefully to notice how Saturn grows slightly in the image as Cassini gets closer to the planet.

March 19, 2004

Date taken: February 29, 2004
Distance from Saturn: 59.9 million kilometers (37.2 million miles)
This week's NASA image was taken by the narrow angle camera on using a special blue filter. Look closely and you'll see that the filter highlights stripes in the atmosphere that either absorb or reflect the blue wavelengths. The reason for the different absorption levels is a mystery. You can also see three of Saturn's moons in the photo including: Enceladus (upper left); Mimas (left of Saturn's south pole) and Rhea (lower right). Look carefully because the moons are tiny compared to the giant planet. To learn more about this image, click here.

March 12, 2004

Date taken: February 23, 2004
Distance from Saturn: 62.9 million kilometers (39 million miles)
This week's NASA release show clumps embedded within Saturn's outer ring (called the F-ring) again taken with the narrow angle camera. The pair of images were taken about 120 minutes apart and show that the clumps revolve about the planet. The clumps are mostly visible in the upper right part of the left image and the lower right part of the image on the right. Saturn's rings remain a great mystery and the Cassini-Huygens mission is designed to help answer questions about the origin, stability and structure of the rings. Clumpiness theories include meteoroid collisions and inter-particle collisions in the outer ring. To learn more about this image, click here.

March 5, 2004

Date taken: February 16, 2004
Distance from Saturn: 66.1 million kilometers (41.1 million miles)
NASA has released another photograph of the planet, taken once again with the narrow angle camera aboard Cassini. It shows only slight variation from the photograph that was released last week. This week's release addresses the composition of the planet's atmosphere -- which is mainly hydrogen. Dark regions show areas of methane mixed with the hydrogen. The lighter areas are high clouds that shield the methane regions at lower altitude. You can see a lot of turbulence just below the equator on the right side of the planet.

February 26, 2004

Date taken: February 9, 2004
Distance from Saturn: 69.4 million kilometers (43.1 million miles)
Today marks the start of the Cassini spacecraft's formal approach to the Saturnian system with the release of the first high resolution color composite image of the planet. This is the point in the Cassini mission at which fine details of the planet's rings, and even atmosphere, are starting to emerge and NASA will be sending along information about the mission with increasing frequency from this point forward. The image was actually taken as a series of exposures and made into this composite color image. The photograph was taken by the narrow angle camera, one of 18 scientific instruments on board the spacecraft. At the time of the photograph Cassini was less than half the distance of the Earth from the Sun (which is 93 million miles -- give or take). The planet has grown 60% in field-of-view size since the last image was taken in November 2003. It only gets more exciting from this point forward.